Concentric tube fuel element spring alignment spacer device



Sept. 24, 1963 5. J. WEEMS CONCENTRIC TUBE FUEL ELEMENT SPRING ALIGNMENT SPACER DEVICE Filed Dec.

INVENTOR. Ste/la? {deems BY W United States Patent CONCENTRIC TUBE FUEL ELEMENT SPRING ALIGNMENT SPAER DEVICE Sterling J. Wecms, Safety Harbor, Fla, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 4, 1961, Ser. No. 157,024

3 Claims. (Cl. 204--193.2)

This invention relates generally to the supporting of nuclear-fuel elements and, more specifically, to a means for yieldably supporting a fuel element in a coolant pasrage.

It is well known in the reactor art to provide radial ribs on fuel elements for supporting them in a coolant passage n a reactor in a radially spaced relation to the passage so hat an annular space is formed between the fuel elenentls and the passage. Coolant may be allowed to flow :hrough this space to remove the heat generated by the 'uel elements durinng reactor operation. See, for extmple, FIG. 39 and column 43 of Fermi et al., U.S. atent 2,708,656, dated May 17, 1955. In the Fermi :onstruction, the supporting ribs are radial projections of he coolant passage which support the fuel element slugs )n all sides. It the fuel elements are to be held tightly n the coolant passage, it may be very diflicult to insert hem into the passage without damaging the ribs or the rassage itself. If the fuel elements become distorted or :nlarged with reactor operation, it may be very difiicult to emove them.

These difficulties and related problems become espezially acute in high performance fuel elements such as in lou ble annular fuel elements for use in the superheatcr egion of boiling-water reactors. In such an application he steam being superheated passes through a longitudinal iassa ge in the inner fuel element and through an annular assage between the inner element and the outer fuel elenent. Problems are encountered in that the rib designs eretoforc known employed to maintain the inner and uter elements in a radially spaced relationship are susepticle to vibration, fretting, and wear of both the ribs nd the cladding of the fuel element upon which the ribs ear. Any distortion, of course, changes the dimensions E the annular steam passage between the inner and outer ements and alters the performance of the reactor.

It is therefore an object of this invention to overcome e difficulties encountered in nuclear-fuel elements disussecl in the preceding paragraphs.

It is another object of this invention to provide a uclear-fuel element suitable for use within a coolant paslge in a nuclear reactor.

It is still another object of this invention to provide a cans of maintaining the concentrioity of the inner fuel ement of a double annular fuel element when operating rdcr such high performance conditions as that enuntercd in the superheater region of a boilingwater retor.

Other objects will become apparent as the detailed deription proceeds.

In the drawings:

FIG. 1 is a longitudinal sectional view, partly in elevaan, showing the rib construction of the present invention applied to double annular fuel elements;

FIG. 2 is a fragmentary elevational view, with parts 'oken away, showing the inner fuel element;

FIG. 3 is a transverse sectional view taken on line 3-3 FIG. 2; and

FIG. 4 is a transverse sectional view taken on line 4-4 FIG. 2.

Referring to FIG. 1, a nuclear-fuel element 10, of the :sent invention, has a plurality of sets of generally lgitudinal, radial ribs 12 and 14, the ribs 12 being 3,165,037 Patented Sept. 24, 1963 mounted on the fuel element so as to be radially movable with respect thereto, and the ribs 14 being attached to the fuel element so as to have no radial movement with respect to the fuel element. In each set, there is one radially movable rib 12 and two fixed ribs 14, and the ribs of each set are about equally spaced from one another peripherally of the fuel element. The rib 12 is connected to fuel element 1% with a wide spiral spring 16 coiled about rib adaptor section 18 of the fuel element. As shown in FIGS. 2 and 3, radially cut guide slots 20 and 22 in the adaptor section 18 receive the end portions 23 of rib 12 and fit the sides of the same so as to allow rib 12 only radial movement through the action of spring 16. Thus, the invention provides for spring-loaded, radially movable ribs for maintaining radial spacing of a fuel element within a coolant passage, said movable ribs serving to hold the fuel element in the desired position While providing for self adjustment should distorting stresses occur during reactor operation.

More specifically, fuel element 1.0 comprises tubular segments 26 of fissionable material within an inner tubular jacket or cladding 28 and an outer tubular cladding 30. The interior and the exterior of the fuel element are circular and cylindrical. The rib adaptor sections 18 are of inert material, separate the segments 26 of fissionable material, and provide mountings for the ribs 12 and 14 and spring 16. Each adaptor section 18 contains a peripheral recess 31 upon which spring 16 is spirally coiled, said recess forming a cylinder of smaller diameter than the diameter of the unrccesscd end portions of the adaptor section 18. The spring 16 is coiled about substantially the entire periphery of the fuel element. Fixed ribs 14 are of a shallow U shape to allow for expansion and compression of spring 16, the base of the U extending across recess 31 and the sides of the U being welded or brazed to adaptor 18 along its unrecesscd periphery. The movable rib 12 is also of a shallow U shape by virtue of its offset end portions 23. The inner edge of the base of the U of the rib 12 is welded or brazed to spring 16 near its outer end. The portions 23 of rib 12 extend longitudinally and radially beyond spring 16 and fit into guide slots 20 and 22, as previously stated. These slots are radially cut, run generally longitudinal according to the positioning of rib 12, and are of such width as to fit the sides of rib 12 and allow bidirectional, radial movement thereof with negligible tangential movement. Longitudinal movement of rib 12 is restricted by the contact of the sides of spring recess 31 with the edges of spring 16.

The ribs 12 and 14 have been described as being geneually longitudinal. This is true in the general sense, and in the more specific sense, the ribs 12 and 14 extend somewhat helically of the fuel element 10 in order to give the fluid flowing over the fuel element a movement about the fuel element as the fluid flows therealong.

As shown in FIG. 1, sets of ribs 12 and 14 may be longitudinally spaced along fuel element 10 at intervals such that structural rigidity will be maintained. It appears that three ribs per set circumferentially spaced substantially degrees apart is a desirable design, but such a configuration is not intended to be a limitation on this invention. Furthermore, the helical cant of the ribs is not a critical feature but is a design characteristic of boiling-water reactors which will be discussed later. The ribs may be positioned in any manner that reactor design considerations may demand as long as they run in a generally longitudinal direction.

The adaptor 18 is provided with fission gas leakage paths 32 so that connecting channels exist through the inert adaptor for gases produced during fission of the fissionable material 26. Thus, the fission gases are allowed to pass to the fission gas reservoir 34.

FIG. 1 depicts the invention as applied to improving the menus of holding the fuel element within an outer tubular fuel element 36. This fuel element comprises fissionnble material 33 within an inner tubular clndding 40 and an outer tubular cladding 42, reinforcing sleeves 44 to strengthen the inner cladding 40 at the regions where the sets of ribs 12 and 14 bear, and a reservoir 46 at the end of outer fuel element 36 for collecting the gases produced in the same during fission. It should be noted that axial movement of fuel element 10 within the fuel element 35 may be prevented by axial pressure applied at the end of element 10, for example, by a spring (not shown).

In applying the fuel-elemcnt configuration discussed above to serve as the fissioncble fuel of a boiling-water reactor, the double tubular assembly comprising fuel elements 10 and 36 is adapted to receive saturated steam at one end and discharge it as superheated steam at the other end after the steam flows axially through a passage 48 in the inner element 10 and an annular passage 50 between inner element 10 and outer element 36. The don lc assembly is adapted to be positioned vertically, along with functionally similar fuel assemblies parallel thereto and spaced therefrom, in a boiling-water reactor in which water is heated to saturated steam outside the outer element 36, and perhaps not directly outside the same, and the saturated steam is converted to superheated steam by passing through the passages 48 and 50. The helical cant of ribs 12 and 14 produces a helical steam fioxv pattern which is expected to reduce thermal distortion of annular passage 50. Boiling-water reactors of the type in question are more fully disclosed in reports GNEC-138 and GNEC-l 50, of General Nuclear Engineering Corporation, available from the Ofiice of Technical Services, Dept. of Commerce, Washington 25, DC. The portions of these reports relating to the claimed subject matter of this application, namely, page 10 and FIG. 2 of GNEE-l38 and pages 111-28 and lV-29 and FIGS. Ill-5, Ill-7, IV-4, lV-6 of GNEC-l50, were disclosed by applicant as his invention to General Nuclear Engineering Corp, his employer, before the reports were written. Reference is also made to Untermycr, US. Patent 2,936,273, dated May 10, 1960, for a basic disclosure of boiling-water reactors.

Each of the fissionuble cores 26 and 38 may be formed of U0 slightly enriched in the isotope U These cores may be formed of a series of relatively short tubular pellets or by vibt'ntory compaction of U0 powder. The jackets 23 and 30 and the spring 16 may be formed of an alloy composed of 76.0% nickel, 15.5% chromium, 1.0% iron. 0.35% manganese, 0.20% silicon, and 0.04% carbon; the jacket 40 and reinforcing sleeves 44 of an alloy composed of 73.0% nickel, 15.0% chromium, 65% iron, 2.3% titanium, 0.9% aluminum, 0.6% columbium, 0.3% silicon, 0.5% manganese, and 0.03% carbon; and jacket 42, adaptor 18, and ribs 12 and 14 of type 347 stainless steel.

Persons skilled in the art will, of course, readily adapt the general teachings of the invention to embodiments 4 other than the specific embodiment illustrated. Accordingly, the scope of the protection afforded the invention is not intended to be limited to the particular e mbocli ment illustrated, but should be determined only in accordance with the appended claims.

What is claimed is:

l. A nuclear-fuel element comprising a cylindrical body, a plurality of fixed radial ribs, a radially movable radial rib, and a Wide spiral spring; said fixed ribs being rigid. generally longitudinal, short in length relative to said body, equal in radial pnojection, attached to the periphery of said body and spaced therearo-und; said radially movable rib being rigid, generally longitudinal, short in length relative to said body, peripherally spaced from said fined ribs, and attached to said spring; said spring being coiled about substantially the entire periphery of body between the same and said radially movable rib; said body having slots therein so as to receive said movable rib and fit the sides thereof to hold the some in a fixed circumferential relationship with said fixed ribs while allowing the movable rib only redial movement.

2. "the nuclear-fuel element according to claim 1, wherein said spiral spring is coiled within a peripheral recess in said body, said fixed ribs extending longitudinally over said recess and being attached to said body at only the unrecesscd portion thereof.

3. The nuclear-fuel element according to claim 2, wherein said plurality of fixed ribs and said movable rib comprise a set thereof, said set being spaced from a like set at longitudinal intervals along the periphery of said fuel element.

References Cited in the file of this patent UNIT ED STATES PATENTS 711,966 Hendrick Oct. 28, 1902 1,049,761 Perkins Jan. 7, 1913 2,035,637 Criclzrner Mar. 31, 1936 2,885,335 Moore et al. May 5, 1959 2,949,415 Stubbs ct al. Aug. 16, 1960 3,030,291 Butler et al Apr. 17, 1962 3,030,293 Wyatt Apr. 17, 1962 FOREIGN PATENTS 213,799 Australia, Mar. 6, 1958 563,703 Belgium July 3, 1958 875,462 Great Britain Aug. 23, 1961 OTHER REFERENCES GNEC-138, Nuclear Superheat Development Program, November 1960, page 10 and Fig. 2.

619851-150, Steam-Cooled Power Reactor Evaluation, Apr. 30, 1961, pp. 111-28 and HI-29 and Figs. III-5, Ill-7, lV-4, and IV-6.

GNEC-l36, A 200 Mw(c) Boiler-Superheater Reactor Preliminary Design, Oct. 25, 1960, pp. 3038 and Figs. 5, 7, and 10. 

1. A NUCLEAR-FUEL ELEMENT COMPRISING A CYLINDRICAL BODY, A PLURALITY OF FIXED RADIAL RIBS, A RADIALLY MOVABLE RADIAL RIB, AND A WIDE SPRIAL SPRING; SAID FIXED RIBS BEING RIGID, GENERALLY LONGITUDINAL, SHORT IN LENGTH RELATIVE TO SAID BODY, EQUAL IN RADIAL PROJECTION, ATTACHED TO THE PERIPHERY OF SAID BODY AND SPACED THEREAROUNG; SAID RADIALLY MOVABLE RIB BEING RIGID, GENERALLY LONGITUDINAL, SHORT IN LENGTH RELATIVE TO SAID BODY, PERIPHERALLY SPACED FROM 